Pollution Prevention Guidelines to provide technical advice and guidance to staff and consultants involved in pollution-related projects. The guidelines represent state-of-the-art thinking on how to reduce pollution emissions from the production process. In many cases, the guidelines provide numerical targets for reducing pollution, as well as maximum emissions levels that are normally achievable through a combination of cleaner production and end-of-pipe treatment. The guidelines are designed to protect human health; reduce mass loadings to the environment; draw on commercially proven technologies; be cost-effective; follow current regulatory trends; and promote good industrial practices, which offer greater productivity and increased energy efficiency.
Table of Contents
- Industry Description and Practices
- Waste Characteristics
- Pollution Prevention and Control
- Target Pollution Loads
- Treatment Technologies
- Emissions Guidelines
- Monitoring and Reporting
- Key Issues
The printing industry is very diverse, as can be seen in the multitude of different products that bear some form of printing—books, daily newspapers, periodicals, packaging, cartons, carrier bags, drink containers, signs, forms, brochures, advertisements, wallpaper, textiles, sheeting, metal foil, and so on. Text, diagrams, pictures, and so on are designed and composed on, for example, a newspaper page. If pictures and/or text are to be printed in several colors, these must be separated.
The pictures are also often screened, producing an image that consists of a large number of very small dots instead of a solid field. Photographic techniques are used for setting and working on pictures. The page is then transferred to a printing form, a printing block (high-intensity, flexography), plate (offset), roller (rotogravure), or stencil (screen printing). This is done by means of exposure to a light-sensitive coating. In the case of offset and screen printing, the printing form is developed by washing away part of the coating; the form may then, in theory, be used immediately.
The offset plate is coated with rubber to protect it from oxidation. The screen sheet’s sides are masked with protective paint. Other printing methods require further stages. The small grooves in the gravure roller are etched or, increasingly, engraved, and the surface is chromed for better durability. The rubber printing block for flexographic printing is cast or engraved by laser.
Printing is done on single sheets or paper web, using one or more printing units, depending on the number of colors required. The dyeing agent is, in most cases, a solvent that evaporates from the paper. (In some cases, it is necessary to hasten evaporation by feeding in warm air.) Clear varnish is sometimes added to the printed surface. The printed matter is processed off-press, where it is cut, jointed, folded, sewn, bound, packaged, and so on.
Printing may also be a step in another manufacturing process—for example, laminating at package printing works, in which layers of paper, plastic and metal foil are joined. Plastic surfaces are treated to facilitate printing using electrical discharges from an electrode system, the “corona treatment.”
Emissions into the air mainly consist of organic
solvents and other organic compounds. Some
substances may cause unpleasant odors or affect
health and the environment.
Discharges to water bodies mainly consist of
silver, copper, chromium, organic solvents, and
other toxic organic compounds.
Noise comes principally from fans, printing
presses, and transport.
Wastes consist of environmentally hazardous
wastes such as photographic and residual chemicals, metal hydroxide sludge, dyestuff and solvent residues, wiping material containing dyes and solvents, and oil spills. There are also bulky wastes such as paper.
Pollution Prevention and Control
The recommended pollution prevention measures are as follows:
- Estimate and control, typically on an annual basis, the quantities of volatile organic solvents used, including the amount used in dyes, inks, glues, and damping water. Estimate and control the proportion that is made up of chlorinated organic solvents.
- Replace solvent-based dyes and glues with solvent- free or water-based dyes and glues, where feasible. Water-based dyes are preferred for flexographic printing on paper and plastic and for screen printing and rotogravure.
- Give preference to the use of radiation-setting dyes.
- Engrave, rather than etch, gravure cylinders to reduce the quantity of heavy metals used.
- Enclose presses and ovens to avoid diffuse evaporation of organic substances entering the general ventilation system, where feasible. Use suction hoods to collect vapors and other fugitive emissions.
- Evacuate air from printing presses and drying ovens into a ventilation system.
- Where possible, replace chemicals used for form preparation and cleaning with more environmentally friendly alternatives. Maintain a record of chemicals and environmentally hazardous waste. Do not use halogenated solvents and degreasing agents in new plants. Replace them with nonhalogenated substances in existing facilities.
- Estimate the quantity of developing bath and fixing bath used per year and maintain these at acceptable levels.
- Minimize the rinse water flow in the developing machines by, for example, use of “stand-by.”
- Collect fixing bath, developer, used film, photographic paper, and blackened ends of photosetting paper and manage them properly.
- Use countercurrent flow fixing processes.
- Aim for a closed washing system.
- Store chemicals and environmentally hazardous waste such as dyes, inks, and solvents so that the risk of spillage into the wastewater system is minimized. Examples of measures that should be considered are retaining dikes or areas with no outlet, as a means of absorbing spillage. Minimize noise disturbance from fans and presses.
- Use equipment washdown waters as makeup solutions for subsequent batches. Use countercurrent rinsing.
- Recover energy from combustion systems, when they are used.
- Return toxic materials packaging to the supplier for reuse.
- Recover plates by remelting.
- Label and store toxic and hazardous materials in secure, bunded areas.